The invention relates to a process for preparing a defined starting operation of a motor vehicle selectable by the driver. The motor vehicle has a starting element arranged between an engine and a transmission. In the event of a maximal power demand by the driver and in the event of the selection of the defined starting operation, the rotational speed or the torque of the engine is set to a specified value via an electronic control unit. The specified value is automatically determined as function of a determined friction parameter, by which at least one relative prediction concerning the transmissible drive torque to be expected for the acceleration operation can be made, such that, by way of this specified value, during the starting and acceleration operation following the preparation, the maximally possible drive torque is achieved for the best possible acceleration.
Such a process is known, for example, in connection with a racing-start starting operation (“launch control”) in the case of BMW M vehicles. This launch control permits an optimal vehicle acceleration on an anti-skid road surface. This known launch control is selected, while the vehicle is stationary, by deactivating the slip control system, selecting a special drive program, moving the selector lever, while the vehicle is stationary, to a defined position and completely depressing the accelerator pedal. Subsequently, the launch control will be prepared by setting the rotational engine speed to a fixed value while the clutch is still disengaged. The vehicle will accelerate with the releasing of the selector lever; i.e. the prepared starting operation will subsequently be continued by means of a clutch control for the purpose of an optimal acceleration.
From German Patent Document DE 103 05 297 A1, a corresponding process is known for controlling a starting operation selectable by the driver, in which case, first, the rotational engine speed (under the condition of an optimal friction) is set to a specified rotational engine speed. During the starting operation, an automatic control of the clutch torque is carried out for achieving a maximum possible acceleration, the engine torque being reduced despite a maximum power demand, when the friction prevailing between the driving wheels and the road is lower than a specified threshold. The circumstance is thereby taken into account that there is actually a lower friction than the assumed optimal friction.
In German Patent Document DE 103 05 298 A1, an alternative process is suggested for taking into account a lower friction. For the preparation of a defined starting operation that can be selected by the driver, while the clutch is disengaged, the rotational speed of the internal-combustion engine is set to a specified rotational engine speed value, in which case, the specified rotational engine speed is determined as a function of at least one parameter, which is formed of at least one known operating variable and by which at least one relative prediction can be made concerning the drive torque to be expected when the clutch is engaged.
For determining the rotational engine speed, a friction parameter, for example, is included. The friction parameter reflects the friction of the tires to be expected on the road. For determining the friction parameter, for example, the ambient temperature, the tire mixture, the vehicle weight, the road type and/or the road condition are taken into account as operating variables. However, the predicted friction parameter may deviate from the actual friction because of various influences that cannot be precisely predicted, so that an optimal acceleration is not achieved.
It is an object of the invention to provide an improved process with respect to the state of the art for the preparation of a defined starting operation selectable by the driver.
This and other objects are achieved by a process for preparing a defined starting operation of a motor vehicle selectable by the driver. The motor vehicle has a starting element arranged between an engine and a transmission. In the event of a maximal power demand by the driver and in the event of the selection of the defined starting operation, the rotational speed or the torque of the engine is set to a specified value, via an electronic control unit. The specified value is automatically determined as function of a determined friction parameter, by which at least one relative prediction concerning the transmissible drive torque to be expected for the acceleration operation can be made, such that, by way this specified value, during the starting and acceleration operation following the preparation, the maximally possible drive torque is achieved for the best possible acceleration. The friction parameter is determined as a function of a state variable determined during a preceding defined starting operation, which state variable influences the occurring drive torque.
The invention takes into account influences when determining the course of the torques, already in preceding defined starting operations, did not result an optimal acceleration of the vehicle.
According to the invention, in a known manner, for the preparation of a defined starting operation selectable by the driver (particularly of a so-called racing start or a so-called launch control) of a motor vehicle, by way of starting element (such as a controllable clutch or a torque converter) arranged between an engine (internal-combustion engine and/or electric motor) and a transmission, in the case of a maximal power demand by the driver and in the case of a selection of the defined starting operation, the rotational speed or the torque of the engine is set to a specified value (rotational engine speed or engine torque) by way of an electronic control unit. In this case the rotational engine speed or the engine torque is automatically determined by the electronic control unit as a function of a friction parameter, by which at least a relative prediction can be made concerning the transmissible drive torque to be expected for the acceleration operation, such that, during the starting operation following the preparation, the maximally possible drive torque is achieved for the best possible acceleration.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.